THE LEGUME POD BORER MARUCA-TESTULALIS, AND ITS PRINCIPAL HOST-PLANT,VIGNA-UNGUICULATA (L) WALP - USE OF SELECTIVE INSECTICIDE SPRAYS AS AN AID IN THE IDENTIFICATION OF USEFUL LEVELS OF RESISTANCE

Cowpea varieties were evaluated for resistance to Maruca testulalis us ing differential insecticide sprays that provided a range of pest dens ities and crop damage. The latter was expressed as a pod evaluation in dex, Ipe, which uses the degree of pod production or pod load (PL) and pod damage (PD). The different spray treatments included a monocrotop hos spray which does not control the pod borer, one or two sprays of a protective mixture of cypermethrin and dimethoate at different stages in the crop phenology, and full protection with the same mixture. Uns prayed cowpea produces very few pods so it was not included as a treat ment. None of the tested varieties was resistant to flower damage, and apart from TVnu 72, the resistant control, none were highly resistant to the borer. Some varieties e.g. MRx nos. 2-85F, 10-85S, 17-85S, 48- 85S, 58-85S, 66-85S, 67-85S and Zonkwa Local had relatively high Ipe v alues, after receiving only one protective spray, and were considered to be moderately resistant. These varieties can either be grown under minimum insecticide protection (i.e. one insecticide spray) to exploit their potential, in the appropriate cropping or agronomic systems whi ch reduce pest densities, or in locations where borer infestation is l ow. The Ipe statistic is related to larval counts in flowers (R(e) = 0 .74-0.79), thus if larval counts in flowers were not taken, it would s uffice as an indirect estimate of the M. testulalis load. This can be done in conjunction with the rapid visual estimate (RVE) of flower inf estation and/or damage which is also more time efficient, even if slig htly less accurate than direct larval counts.